The youngest of 20 children, Fannie Lou was working the fields with her sharecropper parents at the age of six. Amid poverty and racial exploitation, she received only a sixth-grade education. In 1942 she married Perry (“Pap”) Hamer. Her civil rights activism began in August 1962, when she answered a call by the Student Nonviolent Coordinating Committee (SNCC) for volunteers to challenge voter registration procedures that excluded African-Americans. Fired from her job for her activism, she became a field secretary for SNCC and a registered voter in 1963.

In 1964 Hamer became vice-chairperson of the Mississippi Freedom Democratic Party (MFDP), established after unsuccessful attempts by African-Americans to work with the all-white Mississippi Democratic Party. As a leader of the MFDP she gave a nationally televised address to the Credentials Committee at the 1964 Democratic National Convention in which she described incidents of violence and injustice suffered by civil rights activists, including her own experience of a jailhouse beating that left her crippled.

In 1967 Hamer published To Praise Our Bridges: An Autobiography. As a member of the Democratic National Committee for Mississippi (1968–71) and the Policy Council of the National Women’s Political Caucus (1971–77), she actively opposed the Vietnam War and worked to improve economic conditions in Mississippi.